This invention relates to control systems for analytical apparatus. It also relates to automatic liquid samplers, for chromatographic apparatus, of the type including a sampling mechanism and a control system which controls both the sampling mechanism and other functions of the apparatus.
In a known automatic liquid sampler for the routine analysis of similar samples by gas chromatography, the samples are contained in vials carried on a turntable which may be indexed to bring each vial in turn to a sampling position. An injection syringe is lowered until its needle enters the vial at the sampling position and the plunger is then operated to fill the syringe. To ensure complete filling and the absence of air bubbles, the plunger is moved up and down several times. The syringe is then raised to clear the vial, traversed laterally to a position above the chromatograph column, and lowered until the needle penetrates the septum of the column. The plunger is operated to inject the sample into the column and the analysis commences. When the analysis of a given sample is completed, the turntable is indexed to bring a fresh sample to the sampling position and the sequence is repeated.
The various movements of the turntable, syringe body and plunger are produced by solenoid actuators which are energized as required by logic circuits controlled by a program unit including a punched tape reader. The program unit also controls the operation of ancillary apparatus such as chart recorders, integrators etc. responsive to the output of the chromatograph detectors. A plurality of tapes are provided, each punched with a program for the analysis of samples of a given type, and for repetitive analyses a tape may be formed into a closed loop.